The invention is concerned with an article of stationery known as a "letter file", that is a file comprising a cover having a front wing, a rear wing and a spine between the wings, all having side edges and upper and lower edges with the side edges of the spine being connected to, or forming part of, the inner side edges of the wings; the file further comprising a mechanism mounted on a base plate which is attached to the rear wing close to the spine and being arranged to receive and retain thereon punched paper sheets.
The term "mechanism" as used herein is intended to mean a device which comprises (i) two part members each in the form of an arch and optionally, a lever for moving the parts apart, to enable the paper sheets to be placed thereon, (a file with such a mechanism is normally called a "lever arch file") or (ii) one or more ring members having two parts sprung towards each other which are movable relatively by hand or spring operated opening device, or triggers, to permit the paper sheets to be threaded thereon (for convenience herein the term "arch" will be used for both the arches and the ring members--except where otherwise clear from the context), (a file with such a mechanism is normally called a "ring file") or (iii) posts on to which the paper sheets may be carried. The term "inclined" as used herein is intended to mean at an angle other than 180.degree. or 90.degree..
The spine and the wings are often formed from a single sheet of cardboard, having score lines provided, about which the cardboard can fold, to separate the spine from the wings.
Lever arch files and ring files with mechanisms mounted on the rear wing are, and have for many years been, extensively used in commerce for filing and storage of documentation. They are stored vertically, resting on the lower edges of the wings and spine. Such lever arch files and ring files suffer from an important disadvantage, viz when a lever arch file or ring file carries a significant amount of paper, it tends to collapse towards the front wing. This means that the lever arch files are not free standing but have to be supported. The support can be provided by stacking the lever arch files to fill shelves having end walls or by providing rigid, normally cardboard, box-like dust covers into which the files are individually received. In addition an attempt has been made to render the lever arch files rigid by providing slots in the front wing through which the arches can pass to lock the front wing against such movement as will permit collapse of the lever arch file.
Furthermore in U.S. Pat. No. 4,997,207 an elongated member is provided to connect together the free side edges of the wings to form a rigid structure. In U.S. Pat. No. 5,267,804 there is shown a file or binder which is not a lever arch file as defined above in which rigid corner pieces are provided on one wing to butt against the other wing thereby to make the binder self-supporting. U.S. Pat. No. 4,744,689 shows a lever arch file having a closure connected by a hinge to the rear wing of the cover to provide rigidity. The known methods of preventing collapse of lever arch files have, at best, been only partially successful, being expensive and/or inflexible in use.